1. Field of the Invention
This invention relates to nebulisers.
2. Brief Description of Art
Many different types of nebulisers are known for delivering medication directly into the lungs of a patient, usually for treatment of respiratory diseases. Nebulisers normally deliver medication in the form of droplets or a dry powder. In most nebulisers, atomisation of the medicament into a stream of air occurs continuously, regardless of whether the patient is inspiring or expiring. However, the effect of continuous atomisation is that a significant proportion of medication is lost during expiration.
Commonly known nebulisers are either pneumatically operated from a compressed air source connected to the nebuliser which atomises the liquid, or are ultrasonic nebulisers which use a piezo-electric crystal to atomise the liquid. More recently, a mesh-type nebuliser has been developed in which the medication is forced through a fine mesh in order to create droplets of the medication. The optimum diameter of medication particles or droplets is about 1-5 microns. If the particles or droplets are bigger than this, they are likely to be impacted in the airway before they reach the lungs, but if they are smaller than one micron, they tend to be carried out of the lungs again on exhalation without sedimenting in the lungs.
One known nebuliser analyses the pressure changes within the device during the first three breaths to determine an average shape of the breathing pattern. A timed pulse of atomisation is commenced upon start of subsequent inspirations such that atomisation occurs for the first 50% of the inspiration. This is illustrated in FIG. 1 where the breathing pattern and pulse are superimposed. This is effective in reducing the loss of medication during exhalation to about 3%. FIG. 1 shows the breaths in a graph of flow rate against time. When the treatment is commenced, a patient breathes in and out three times through the nebuliser before treatment commences. The first three breaths are measured so that the timed pulse of atomisation occurs for 50% of the average time of inhalation. The duration of inhalation is indicated as T1, T2 and T3. These timed periods are averaged, and divided by two in order to determine the pulse length for the next fourth breath where treatment starts. For each subsequent breath, the duration of the pulse of atomisation is determined by summing the time period of inhalation of the previous three breaths, dividing by three to obtain an average and dividing by two. The dose administered to the patient is directly proportional to the duration of the pulse of atomisation, and so the period of atomisation is summed, and the atomiser is switched off, or indicates that the patient should stop once the dose administered to the patient reaches the amount of medication prescribed for that treatment.
Other nebulisers are known in which the timed pulse of atomisation is other than 50% of the duration of inspiration. However, in these other nebulisers, the pulse length must be set for each patient by the clinician. Many of the nebulisers are, therefore, suitable only for use in a controlled environment, such as a hospital. The setting of the pulse length for each patient means that most nebulisers are not suitable for a patient to use at home.
Reference is made to International Patent Publication No. WO 97/48431, the contents of which are hereby incorporated by reference in its entirety. In addition, FIGS. 2 and 3 of this application show the nebuliser which is disclosed in the above International Patent application. Referring to FIG. 2, a mouthpiece 1 is shown through which a patient inhales in the direction of arrow 2. Below the mouthpiece 1 is a removable atomising section 3 which, in turn, rests on a base 4.
The base 4 is shown in more detail in FIG. 3. Referring to FIG. 3, the base 4 includes an inlet 5 through which air is supplied under pressure from a compressor (not shown). The pressurized air is led via a tube 6 to a manifold 7 which controls the flow of pressurized air to an air outlet 8 which directs air into the atomising section 3 shown in FIG. 2. The base 4 also includes a pressure sensor 9 which detects the pressure within the atomising section 3 via a port 10 electronic circuitry and a battery. The port 10 connects the pressure sensor 9 to the inside of the mouthpiece. This is attached to a printed circuit board 17 which is powered by the battery 19. When the pressure sensor detects that a patient has inhaled, the electronic circuitry controls the manifold 7 to divert pressurized air to the air outlet 8.
Referring again to FIG. 2, air under pressure passes through the air outlet 8 of the base 4 and is conducted through a tubular post 11 to an atomiser nozzle 12 out of which the air issues under pressure. A deflector 13 is located in the path of the pressurised air issuing from the nozzle 12 so that the pressurized air is deflected laterally so as to pass beneath a baffle 14. The passage of the pressurized air across the top of the tubular post 11 causes medication 15 to be drawn up between the outer surface of the tubular post 11 and the inner surface of a sleeve 16 which surrounds the tubular post 11. The medication 15 is atomised in the stream of air, and carried away in the stream of air below the rim of the baffle 14 and up through the mouthpiece 1 to a patient.
The pressure sensor 9 in the base 4 monitors the breathing pattern of a patient, and on the basis of the breathing pattern, the manifold 7 is controlled by the electronic circuitry to supply pressurized air to the atomising section 3 only during the first 50% of an inhalation phase incorporated in WO 97/48431.
According to a first aspect of the present invention, a nebuliser comprises means for determination of the duration of a pulse of atomisation during inspiration, the determination means including means for measuring the tidal volume of a patient, timing means for measuring the duration of inspiration, means for storing an estimate of the volume of a patient""s upper airway, and means for calculating the duration of the pulse on the basis of the tidal volume measured by the tidal volume measuring means, the duration of inspiration measured by the timing means, and the stored estimated volume of a patient""s upper airway from the storage means.
According to a second aspect of the invention, a method for determining the duration of a pulse of atomization during inspiration during operation of a nebuliser comprises:
(i) measurement of the tidal volume of a patient;
(ii) measuring the duration of inspiration of a patient;
(iii) storing an estimate of the volume of a patient""s upper airway; and
(iv) calculating the duration of the pulse on the basis of the measured tidal volume of the patient, the measured duration of inspiration and the stored estimated volume of the patient""s upper airway.
The means for calculating the duration of the pulse on the basis of the tidal volume is preferably comprised of a microprocessor, and the microprocessor might also be one of the elements of the tidal volume measuring means. The means for measuring the tidal volume of a patient includes a breathing sensor, which is preferably a peak flow sensor, but could be any one of a number of known sensors such as a pressure sensor. If a pressure sensor or the like is used, the microprocessor can determine to flow rate of each breath from the output of the sensor. From the sensor output it can determine the tidal volume. Associated with the microprocessor is an electronic memory in which data is stored, and in which is stored an estimate of the patient""s upper airway, thereby constituting the means for storing an estimate of the patient""s upper airway.
In this document, the upper airways of a patient are the mouth and trachea, and preferably include the volume of the nebuliser chamber.
The determination of the length of pulse of atomisation enables the proportion of the inhalation time during which atomisation occurs to be extended above 50% towards 100%. This will result in the patient receiving their treatment in a shorter time, since it will take fewer breaths to deliver the required dose of medication. However, there is no point in continuing atomisation into air which is inhaled by the patient at the end of his or her inspiratory phase (the xe2x80x98end volumexe2x80x99), since it will remain in the upper airways. The medicine which does not go beyond the upper airways will be wasted when the patient exhales.
Thus, the invention according to the first and second aspects enables a pulse of atomisation to be generated which is longer than 50% but which stops atomisation before the end volume of inspiration begins. Another advantage of this invention is that a patient""s adherence to the treatment regime will be much improved if the length of treatment is reduced.
In addition, the invention allows automatic optimisation of the pulse length without needing to be set by a clinician. This means that the pulse length will automatically be adapted to each patient on the basis of the patient""s breathing pattern at the time the medication is being administered. Thus, the nebuliser may be used by the patient outside of the controlled environment of a hospital, and may be used at home. In addition, it is possible for the device to indicate when a dose has been administered without the patient needing to count the number of breaths which he or she has taken from the nebuliser.
According to the preferred embodiment, the means for measuring the tidal volume of a patient includes means for measuring a patient""s peak flow, and tidal volume prediction means for calculating the tidal volume on the basis of the peak flow from the peak flow measuring means, and the duration of inspiration measured by the timing means. The means for measuring the patient""s peak flow is a peak flow sensor or an airflow sensor such as a pressure sensor, the output of which is received by the processor. If the sensor is a pressure sensor or the like, the sensor identifies the peak pressure to determine the peak flow. The processor is the tidal volume prediction means.
Some or all of the values used in the calculations are mean values derived from a number of earlier measurements of each breathing pattern of the patient. For example, the patient will start inspiration through the nebuliser, and atomisation will not occur during the first three breaths. The first three breaths are analyzed by the nebuliser by recording the duration of inspiration, and the peak flows during inhalation as are required to determine the duration of a pulse of atomisation. Atomisation takes place on the fourth and subsequent breaths, in each case the values in the calculations are derived from a number of earlier measurements of the inspiration phase of a patient, in this case the previous three inspiratory phases.
Preferably, the atomisation is caused by a stream of gas under pressure passing through the nebuliser and sourced from a gas supply means. This gas is normally air, and the source is preferably a compressor operating together with an accumulator. During atomisation, gas from the accumulator is used to atomise the medication, and the compressor generates air under pressure to fill the accumulator. If a patient""s inspiration is very long, the accumulator may be caused to be emptied, thereby disrupting atomisation. The atomiser, therefore, preferably includes a means for limiting the duration of the pulse so as to maintain the accumulator in a state where it is always under some pressure. In addition, the accumulator may include a valve which, when the accumulator is fall, vents gas to atmosphere thereby preventing it from becoming dangerously full. It is often preferable to maintain the compressor in operation all the time and to vent excess air to atmosphere rather than to switch the compressor on and off.
According to a third aspect of the present invention, a nebuliser comprises means no for predicting the tidal volume comprising means for measuring a patient""s peak flow, timing means for measuring the duration of inspiration, and tidal volume prediction means for calculating the tidal volume on the basis of the peak flow from the peak flow measuring means, and the duration of inspiration measured by the timing means.
According to a fourth aspect of the invention, a method of predicting the tidal volume of a patient comprises:
(i) measuring a patient""s peak flow;
(ii) measuring the duration of inspiration of a patient;
(iii) calculating the tidal volume on the basis of the measured peak flow, and the measured duration of inspiration of the patient.
Measuring the patient""s respiratory volume (tidal volume) has previously involved continually monitoring the patient""s inspiratory flow, typically every ten milliseconds. The flow rate is integrated over the duration of inspiration to determine the inspiratory volume. However, the third and fourth aspects of the invention determine the tidal volume of a patient much more simply. This invention reduces the amount of data processing which is required, thereby reducing the cost of the overall nebuliser. The peak flow is much simpler to measure, and can be used more simply in a calculation to determine the tidal volume.